We have found that postnatal experience with an odor leads to an enhanced uptake of 14C 2-deoxyglucose in specific glomeruli in the olfactory bulb of young rats. We will investigate this phenomenon in several ways. We are first interested in the importance of the circumstances under which the odor is experienced for the induction of the enhanced neural response. We will then investigate the mechanism by which the neural alterations occur. Specifically, we will test the efficacy of different odors and odor concentrations. We will then determine the temporal parameters of the experience in the development and retention of the enhanced neural response. We will then determine the importance if maternal presence in inducing the neural response. The ability of odor exposure in different learning situations will then be assessed. The mechanisms that will be tested include: development of a differentially projecting olfactory field, differential glomerular size, differential mitral cell survival and differential mitral cell dentritic arborization. The thermal basis of mother-young interactions in Norway rats will also be investigated during the next year. Specifically, we will investigate the importance of the rise in brain temperature that we have found to be associated with the termination of the contact bouts between mother and litter. We will first determine the brain temperature response when mothers are faced with potentially different heat loads in different ambient temperatures, with litters of different sizes, with older litters, as well as with nests. We will also determine whether the mothers lose control of their brain temperature when they enter a period of REM sleep while they are with their pups. We will then determine the importance of steroid hormones in elevating maternal thermal set point for elevating maternal heat production and for suppressing heat loss.